It took three seasons, but Agents of SHIELD's FitzSimmons is finally all systems go. It's never smooth sailing for the science wonder twins, however, and Simmons new job could send the fan-favorite 'ship into rough seas.

A new Director (played by Jason O'Mara) will arrive on the scene as season 4 begins, and Coulson's (Clark Gregg) team will close ranks against the newcomer. Simmons (Elizabeth Henstridge), however, will find herself playing confidant to the new boss.

"Agent May (Ming-Na Wen) is tasked with training specialist strike teams, and Fitz (Iain De Caestecker) and Simmons have taken a big step forward in their relationship," ABC teased. "But with Simmons' new promotion as Special Advisor to the Director in Science and Technology, Fitz, as well as her former team members, finds it hard to confide in or trust her since she's now the Director's confidant."

As the season plays out, viewers will get to see how Fitz and Simmons deal with their differences now that their individual decisions have a greater impact on each other. After all, it's not like they haven't disagreed in the past (i.e. the Inhuman dilemma).

"I'm kind of curious to see how that's going to affect them now that they're in a romantic relationship, because for them the stakes are really high," Henstridge told Enstars at San Diego Comic-Con. "They've gone through so much; they've crossed so many hurdles. They have given up a lot to be with each other and worked through a lot, so I think we'll just see kind of how they navigate the relationship journey."

Tune in to the season 4 premiere to find out just how far FitzSimmons will have come in their relationship. Catch Agents of SHIELD Mondays at 10 p.m. ET on ABC. Click the video below to see a preview for the series' latest episode.